Various types of networks exist and mobile stations operate in different operating modes within these networks. For example, mobile stations sometimes operate in Enhanced General Packet Radio Service (EGPRS)-compliant, General Packet Radio Service (GPRS)-compliant, and Universal Mobile Telecommunications Service (UMTS)-compliant modes. Some modes have advantages over others under different conditions. For instance, the UMTS mode offers higher bandwidth and throughput than EGPRS and GPRS. The EGPRS mode allows the use of higher coding schemes providing for the more efficient transfer of data when compared to GPRS.
In many modes of operation, data blocks are transmitted through networks, but sometimes have to be retransmitted when the blocks become lost or misplaced. A packet scheduler is used to transmit the data blocks, but this scheduler and the mobile station to which the blocks are ultimately being sent are often separated by several network entities and an air interface. Consequently, a substantial time delay is usually present. The delay necessitates that the packet scheduler send downlink data blocks in advance of the amount of time equal to the downlink propagation delay such that there are almost always downlink data blocks transiting to the mobile station.
Previous approaches have not allowed mobile stations to fully utilize the benefits of operating in some operating modes, such as the EGPRS-compliant mode. Specifically, the Radio Link Control (RLC) and the Medium Access Control (MAC) layers in EGPRS/GPRS systems use a sliding window protocol to track segmented blocks while in transit. To keep the window moving, acknowledgements must be frequently requested by the packet scheduler. These acknowledgements erode the uplink throughput, which is needed for uplink data transfers. Since the amount of delay is large between the scheduler and the mobile station, it is very costly whenever a data block is missed and retransmission is required. In the case of EGPRS-compliant mobile stations, these mobiles cannot gain all the benefits of incremental redundancy resulting in the inability to use high EGPRS coding schemes.
In other previous approaches, when an EGPRS-compliant mobile station in the downlink direction is multiplexed with a GPRS-compliant mobile station in the uplink direction, the EGPRS-compliant mobile station often transfers data blocks at a lower channel coding scheme even when Radio Frequency (RF) conditions would permit a higher channel coding scheme. Consequently, the higher coding schemes used by EGPRS-compliant mobile stations cannot be used.
In addition, EGPRS-compliant mobile stations require more memory than GPRS-compliant mobile stations in order to accommodate larger window sizes and support higher coding schemes. This requirement results in the multi-slot capacity of the EGPRS-compliant mobile stations being reduced as compared to the GPRS-compliant mobile stations. Consequently, the mobile stations operating in EGPRS mode transfer data at a lower bandwidth and lower coding scheme thereby reducing the throughput of data transferred.
Furthermore, when the packet scheduler in a EGPRS/GPRS network is separated from the mobile station by several network entities, the packet scheduler may be connected to other network entities via different types of links such as E1 cables. The bandwidth available over these E1 cables (backhaul bandwidth) may be reduced due to cost constraints with the operator. This causes limitations to the rate at which data is transferred to mobile stations.
All of these problems result in less than optimal performance for mobile stations when operating in modes such as EGPRS mode. Less system throughput, slower communications, and/or increased user frustration often results because of these shortcomings.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.